If risks are overstated, this may cause unwarranted psychological stress, which itself may constitute or cause a significant and measurable health impact among the public. Effective hazard communication must therefore steer a course between causing complacency and causing alarm. On the other hand, the phenomenon of information-induced health problems should never be cited as grounds for withholding information from the public, where that information could enable appropriate precautionary action to be taken to mitigate a significant threat to health or the environment.
Perhaps the greatest challenge in risk communication is in situations where there is uncertainty about the level or nature of the risk. Although hazard assessment can often be undertaken with high levels of scientific certainty, risk assessment relies to a greater extent on model assumptions, and therefore the levels of uncertainty - and the scope for producing widely differing assessments of risk - is far greater. It is crucial that risk communication fully respects the precautionary principle in the light of any such uncertainties, and that any realistic doubts and gaps in knowledge are communicated to the public.